The present invention relates generally to the field of catheters. More specifically, the present invention relates to dilatation catheters for use in administering treatments to relieve a stenotic region or to widen a constricted blood flow or tubular passage, such as the coronary artery, as well as other vessels.
Percutaneous transluminal coronary angioplasty (PTCA), a procedure for treating a patient having a stenosis or constricted blood region in a coronary artery, has become a widely accepted therapeutic alternative to coronary arterial bypass surgery for many patients. PTCA increases the lumen by radial expansion. The main advantage of PTCA rests in the avoidance of the immediate post-operative discomforts associated with coronary bypass surgery, and certainly in the reduction of morbidity by use of this procedure.
The benefits of PTCA are restricted to lesions accessible to the balloon dilatation catheter. With standard systems, certain lesions are inaccessible due to variations in the patient's anatomy and vasculature. Further, seducing side branches, tortuous vessels, and the more distal arteries have presented serious difficulties in the PTCA procedure because, due to its cross-sectional area, the balloon could not reach the stenotic region.
Performing a coronary angioplasty involves the difficulty of inserting a balloon catheter into the desired coronary artery. Most balloon catheters are too flexible for direct insertion into the patient's coronary artery. Accordingly, the standard angioplasty process begins with the insertion of a guiding catheter, or sleeve into the obstructed vessel, under local anesthesia. To facilitate the introduction of the guiding catheter, and to avoid damage to the body lumen at the puncture site, a guide wire may be useful in the insertion of the guiding catheter. The guiding catheter is designed to provide a conduit through which a balloon catheter is not tapered so as to permit the unimpeded passage of the balloon catheter therethrough.
When considering angioplasty as a method of treating stenotic regions, the morphology of the lesion is critical in determining whether the balloon catheter can be safely passed beyond the stenosis, and whether the vessel will adequately dilate. If the stenosis is comprised primarily of fatty deposits, for example, it is often times possible to compress the stenosis radially outwardly, against the adjacent vessel wall, so as to increase the cross-sectional area of the vessel, and provide adequate perfusion through the vessel. If, however, the artery is hard, or the stenosis has calcified, a standard balloon might burst when inflated. Further, tortuous hardened arteries may be dissected if inflated with such a dilatation balloon.
The lesion may be approached with a guide wire by advancing the catheter and guide wire as a unit, or by advancing the guide wire first. Steering the tip of the wire is done by the surgeon or by an assistant. If the tip is moving in an undesired direction, then slight withdrawal and rotation of tip will point it in the correct way. Once the wire is positioned, the balloon catheter may be advanced over it until it crosses the lesion while the surgeon pulls back on the guide wire to maintain the tip in a fixed position in the distal coronary. If resistance is encountered at the lesion, gentle pressure on the balloon catheter will often cause it to cross. If, however, the lesion is too tight or hard and the balloon tip still will not cross, a new, low profile catheter must be selected. In this instance, the safety of the movable guide wire system must be sacrificed.
Ordinarily, a cardiologist, administering an angioplasty treatment, does not know how much pressure to apply to the balloon to achieve satisfactory results. Since the balloon is non-distensible, it can be inflated only to the constructed size of the balloon. Further attempts to force fluid into the balloon will result in increased pressure, but no significant increase in diameter. However, excessive pressure in the balloon may dissect the artery, which may cause serious damage to the patient's heart.
Therefore, the cardiologist positions the balloon in the artery, expands the balloon, and then allows the balloon to depressurize to permit measurement of blood flow across the stenosis. If the blood flow rate is not acceptable, the cardiologist must repeat the angioplasty treatment, often times necessitating the insertion of multiple catheters, of progressively larger diameters, to gradually increase the lumen of the artery until the obstruction is either alleviated, or until the cardiologist determines that angioplasty will be unable to restore the blood flow rate to an acceptable value.
When the angioplasty procedure requires the insertion and withdrawal of a great many balloon catheters, the risk of damage to the lining of the blood vessel is substantially increased. All blood vessels have a lining of very flattened cells, known as endothelial cells, the integrity of which is essential to normal blood flow. Damage or injury to the endothelial layer promotes the adherence of blood cells passing through the vessel at the point of injury, and may form further obstructions within the artery or vessel.